Numerical Simulation Investigation of a Double Skin Transpired Solar Air Collector

Transpired solar collectors (TSC) are one of the most popular solar thermal technologies for building façades. TSC use solar energy to heat the absorber surface, which transmits thermal energy to the ambient air. A variant of TSC, namely, a double skin transpired solar collector (DSTSC), has been analyzed in this paper, thus providing guide values and a technical point of view for engineers, architects, and constructors when designing such transpired solar collectors. Three important parameters were addressed in this study through numerical simulation: the influence of a separation plate introduced in a TSC, turning it into a DSTSC; the air layer thickness influence on the performance of the collector; and the influence of the used absorber materials for the separation plate material. Greater heat exchange efficiency was noticed for the DSTSC at every imposed airflow rate compared with the TSC. Regarding the thickness of the collector, the efficiency gradually increased when increasing the solar collector thickness until it reached a value of 20 cm, though not varying significantly at a thickness of 30 cm.

The Effect of Variations of Flow from Tributary Channel on the Flow Behavior in a T-Shape Confluence

Channel confluences are of the common structures in fluid transport channels. In this study, a series of numerical simulations were performed, utilizing a 3D code to investigate the reaction of the flow parameters and vortical structure to the variations in flow discharge and its Froude number from both main channel and tributary branch in a T-shape junction. The code was calibrated with the experimental data. Parameters, including the velocity, the turbulence energy, stream surface profile, head losses, and the transverse flow motions, were considered in different situations. It was concluded that increasing the ratio of discharge of flow from side-channel to the main channel (Q*) increased the area and power of the recirculation zone, as well as the width of separation plate downstream of the confluence, while it reduced the area of the stagnation zone (or the wake vortex) within the side-channel. It was also indicated that increasing the discharge ratio from side-channel resulted in an increase in the upstream water level in the main channels, which was dependent on the upstream discharge.

Comparative study of heat transfer enhancement on liquid-vapor separation plate condenser

Basic structures of liquid-vapor separation cooling plates (LSCPs) and a liquid-vapor separation plate condenser (LVSPC) are innovatively designed. Strengthening heat transfer principle of the LSCPs is demonstrated by theoretical analysis. The average condensation heat transfer coefficients (ACHTCs) of the LSCPs are calculated and compared with conventional cooling plate (CCP). Results show that for a laminar flow, the ACHTCs of 2-parts liquid-vapor separation cooling plate and 3-parts liquid-vapor separation cooling plate are respectively 19% and 32% higher than the ACHTCs of the CCP in the same conditions. The ACHTC ratio of N-parts liquid-vapor separation cooling plates (NLSCP) to CCP is $\sqrt[4]{N}$in the same conditions. For a turbulent flow, results show the smaller the height of condensation area, the greater the ACHTCs of cooling plate. In the LVSPC study, operation conditions include the refrigerant R134a mass flux ranging from 22 to 32 kg/(m2.s) and inlet vapor quality from 0.5 to 1 for the saturated temperature of 40∘C. Calculation results showed that the ACHTCs of the LVSPC are 6–24% higher than the ACHTCs of the given common plate condenser (CPC), and similar to the CPC, the ACHTCs of the LVSPC increases with the increase of mass flux and vapor quality.

Using High-Speed Nasopharyngoscopy to Quantify the Bubbling Above the Velopharyngeal Valve in Cases of Nasal Rustle

Objective: The loud and severely distorting form of audible nasal emission (commonly known as nasal turbulence or nasal rustle) typically occurs with a small velopharyngeal opening during production of pressure-sensitive consonants. The purpose of this study was to determine whether bubbling of the secretions, which commonly occurs on the superior aspect of the velopharyngeal port when there is a small opening, is a periodic process that can generate sound in the nasal cavity. Participants: Ten pediatric patients were included in the study. All participants had normal articulation and resonance but exhibited audible nasal emission characterized as nasal rustle. Measures: For each participant, high-speed video (HSV) nasopharyngoscopy and acoustic signals were recorded simultaneously. The acoustic recordings were captured in a manner similar to nasometry using nasal and oral microphones connected to a separation plate. Spectral analysis of the audio recordings and the HSV images was used to determine correlation between the acoustic and visual measurements. Results: This study showed that secretion bubbling is a periodic process and its frequency, measured from the HSV data, was also captured by the acoustic measurements. The nasal acoustic signal correlated more strongly with the video of bubbling than the oral acoustic signal in the majority of the cases where bubbling occurred. Conclusion: These findings are strong evidence that secretion bubbling plays a significant role in the mechanism that generates undesired sound in the nasal cavity. Further work is needed to determine whether this sound is perceived as nasal rustle.

Reduced-order analysis of an oil-fuel furnace vibration and comparison with the finite element method

Thermoacoustic oscillation occurs in modern industrial furnaces, gas turbines, and liquid rockets. However, the thermoacoustic prediction tools for furnaces vibration are less developed. This paper presents a one-dimensional (1D) linear acoustic approach to analyze the three-dimensional acoustic modes of a 660 MWe oil-fuel furnace. The interaction between the flame and acoustic field is described with the flame transfer function. The global time delay is evaluated through a Reynolds averaged simulation. The results of the 1D acoustic approach are compared with real furnace test data. The unstable modes are close to the natural modes of the furnace, and the 30 Hz in the longitudinal mode is the strongest vibration frequency. The effects of inlet length reduction and separation plate removal are also examined. When the separation plates are removed, the time lag of flame in response to inlet flow decreases from 52.5 milliseconds (ms) to 43.8 ms. The results of the 1D approach and finite element method (FEM) show a same safe operation window. The reduced-order procedure and FEM adopted in this study give us a solution to mitigate the vibration in the furnace.

The Effect of Nasal Decongestion on Nasal Patency and Nasalance Scores in Subjects with Normal Speech

Objective: The objective of this study was to evaluate the effects of pharmacological decongestion on nasalance scores. Participants: The participants were 20 adults with normal speech and resonance. Methods: Nasal patency was first determined by measuring the mean minimal cross-sectional area of the nasal passages by acoustic rhinometry. Each participant then read two passages as two predecongestion nasalance scores were obtained. A nasal decongestant was then administered to each nostril without removing the separation plate. Ten minutes later, nasalance scores were repeated. Finally, the separation plate was removed and the mean minimal cross-sectional area was obtained again. Main Outcome Measures: The outcome measures were the pre- and postdecongestion measurements of nasal patency and nasalance scores. Results: Minimal cross-sectional area increased significantly from 0.53 cm2 before decongestion to 0.66 cm2 after decongestion. For the Turtle Passage, the group mean nasalance for the two predecongestion measures (10.70% versus 11.55%) were significantly different and the pre- versus postdecongestion measures (10.70% versus 12.15%) were also significantly different. For the Mouse Passage, the group mean nasalance scores for the two predecongestion measures (32.10% versus 32.00%) were not significantly different but the pre- versus postdecongestion means (32.10 versus 34.40) were significantly different. Correlation coefficients showed a negligible relationship between measures of nasal patency and nasalance scores for both stimulus passages. Conclusions: Nasalance score variability was small and not meaningful for standard clinical purposes. The correlation between nasalance scores and nasal patency was weak.